1. Field of the Invention
The present invention relates to nonlinear optical systems, and particularly to compositions capable of second harmonic generation.
2. Background of the Invention
The high light intensities available in coherent laser radiation have led to the development of nonlinear optical systems. The optical properties of materials are different at high intensities, since the electronic oscillators are driven so hard that anharmonic properties become evident. One such effect is harmonic generation of light, for example, conversion of red laser light to ultraviolet radiation of exactly doubled frequency. This effect, known as second harmonic generation, was first observed when quartz crystals were illuminated by laser radiation. Since this discovery, a number of inorganic and organic materials capable of second harmonic generation (SHG) have been discovered. A useful review of the state of the art relating to nonlinear properties of organic materials is provided by Williams, ed., Nonlinear Optical Properties of Organic and Polymeric Materials, (American Chemical Society, 1983).
It has been found that a multiphase heterogeneous composition containing polymeric material and pyrilium dye can be used to control bulk nonlinear optical properties. The composition exhibits large nonlinear polarizability, self-dipolar alignment and second order nonlinear optical properties in thin film form. Second order nonlinear optical properties of the composition include second harmonic generation, sum and difference frequency mixing, and electrooptical effects.
U.S. Pat. No. 3,615,414 issued to Light discloses a multiphase heterogeneous composition formed from an organic dye and electrically insulating polymeric material. A solution of dye and polymer is exposed to a solvent to form heterogeneous compositions. The compositions are said to be useful as photoconductors or electrophotosensitizers and are characterized by a radiation adsorption maximum that is substantially shifted from the adsorption maximum of the dye dissolved in the polymer to form a homogeneous composition. Particularly useful dyes are said to be pyrilium dyes.